<!DOCTYPE html>
<title>A smooth scroll operation in load event handler isn't omitted</title>
<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
<link rel="help" href="https://drafts.csswg.org/cssom-view/#concept-smooth-scroll">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="support/scroll-behavior.js"></script>
<style>
  body {
    margin: 0;
  }
  html {
    overflow: auto;
  }
</style>
<div id="pageContent" style="position: absolute; left: 0; top: 0;"></div>
<script>
  window.addEventListener("load", () => {
    // Expand the page content to make the root scroll container overflowed.
    pageContent.style.width = (window.innerWidth) * 5 + "px";
    pageContent.style.height = (window.innerHeight) * 6 + "px";

    promise_test(async () => {
      document.scrollingElement.scrollTo({
        left: window.innerWidth,
        top: window.innerHeight,
        behavior: "smooth"
      });

      assert_equals(document.scrollingElement.scrollLeft, 0, "Should not set scrollLeft immediately");
      assert_equals(document.scrollingElement.scrollTop, 0, "Should not set scrollTop immediately");

      // In the next frame, change something to trigger a paint which might
      // clobber the smooth scroll operation.
      await new Promise(resolve => requestAnimationFrame(resolve));
      pageContent.style.color = "green";

      await waitForScrollEnd(document.scrollingElement);

      assert_equals(document.scrollingElement.scrollLeft, window.innerWidth, "Final value of scrollLeft");
      assert_equals(document.scrollingElement.scrollTop, window.innerHeight, "Final value of scrollTop");
    }, `Smooth scroll in load event handler`);
  });
</script>
